Bean angular leaf spot caused by Phaeoisariopsis griseola is one of the diseases that cause the highest yield looses in common beans (Phaseolus vulgaris) in Latin America, because of its consistent increase in incidence and severity. Normally, infection occurs after the fourth week of the crop, causing leaf necrotic lesions, chlorosis and early defoliation, all of which reduce yield significantly. The populations of this fungus have shown large pathogenic variability, presenting pathotypes with a high degree of adaptation to the genetic pool of the host as a result of the process of coevolution. The present study had the objective of studying the pathogenic variability of the fungus P. griseola based on monosporic isolates from bean growing regions in Costa Rica. A population of 61 isolates was inoculated over the group of angular leaf spot differentials, which is formed by Andean and Mesoamerican bean landraces or varieties. A total of 21 pathotypes was identified based on the phenotypic reaction of differentials out of those races 0-0 and 0-53 were the most frequent and geographically widespread. Races 20-21, 8-0, 42-57, and 52-57 were the less frequent races. The Mesoamerican differentials were more susceptible to the fungus, however, no specificity was detected in the isolates because several of the Andean differentials were also susceptible to the pathogen. The results suggest the importance of knowing the variability of P. griseola in the establishment of breeding programs and incorporating durable resistance through either gene pyramiding or deployment.
Phaseolus vulgaris; bean disease; plant breeding; coevolution
